Process of winning elemental phosphorus



July 28, 1959 l.. BuRGEss PROCESS OF WINNING ELEMENTAL PHOSPHORUS 2 shets-sneet 1 Filed Aug. 25 195.5

u u m INVENTOR LOU/S BURGESS TTORNEY July 28, 1959 L.. BuRGEss 2,897,057

PROCESS OF WINNING ELEMENTAL PHOSPHORUS v Filed Aug. 2s, 1955v 2 sheets-'sheet -2 INVENTOR LOU/5" BURGESS l tical electrodes.

United States Patent Opce p 2,897,057 Patented July 28, 1959 PROCESVS OF WINNING EIJENEENTAL PHOSPHORUS Louis Burgess, Jersey City, N.J.,lassignor to lSam Tour and himself; MurrayV Burgess and Eddie Burgess Beitler, executors of saidfLouisBurgess, deceased Application August 2S, 1955, Serial No. '530,507

`1'5 Claims. (Cl. 23-223) This invention is a new and useful process of winning elemental phosphorus. It is a continuation-in-part of my co-pending application, Serial No. 442,639, tiled July 12, 1954, now abandoned, and will be fully understood from the following description read in conjunction with the drawings in which:

Fig. 1 is a diagrammatic elevation of apparatus in which the invention may be carried out;

Fig. 2 is a section through the construction shown in Fig. 1 on the plane indicated by 2 2;

Fig. 3 is a diagrammatic elevation of apparatus in which an embodiment of the invention may be carried out; and

Fig. 4 is a section through part of the apparatus shown in Fig. 3 on the plane indicated by 4 4.

Elemental phosphorus was first commercially produced from phosphorus ore (so-called phosphate rock) in a blast furnace. The phosphate rock and coke .for reduction, together with excess coke to support combustion, was charged to the furnace in which it was heated by direct contact with burning coke and combustion gases. The phosphorus was taken overhead in admixture with the large volume of combustion gas produced and the oxide residue in liquid phase was tapped from the base of the furnace. The process was wasteful of fuel since the reduction occurred principally in the pool of liquid in the base of the furnace. Recovery of the phosphorus Was complicated by the large volume of dilu-y ent gas. The presence of the phosphorus in the combustion gases made it dicult, if not impossible, to recover the heat units present.

This process was superseded by the electric furnace process in which a charge of phosphate rock and carbon is heated in an electric furnace of the arc type with ver- The phosphorus, ltogether with the carbon monoxide simultaneously produced by reduction, is taken overhead and the oxide residue in liquid phase tapped out of the base of the furnace.

The consumption of electricity in the electric furnace process is relatively high.

In both processes tapping the oxide residue at lthe high temperature involved requires skilled labor and is therefore expensive. The efforts of numerous researchers have been devoted for many years to eliminating these difculties but without success.

One object of the present invention is the continuous mechanical removal of the exhausted residue of reaction. Another is the elimination, or in one embodiment, the substantial reduction of the electric current required.

The process by which I accomplish these objects is broadly as follows:

(a) I form a coke throughout which the ore is disseminated in the form of particles in a supporting structure of carbon and in which the carbon is in excess of that consumable by reduction of the phosphate rock and other reducible substances present;

(b) I heat the coke so formed out of directV Contact with combustion .gases to the temperature at which reduction of the phosphate rock by carbon proceeds, conducting away the carbon monoxide and phosphorus in gas phase resulting from the reduction;

(c) The residue of excess carbon and inorganic oxides is removed from the heating zone in solid form.

It isa characteristic of the instant. process that the carbon lin the coke structure, in which the oxide is disseminated, is in excess of that consumable in the reduction. The eifect of this is to hold the'oxide particles apart up to the point of complete reduction, and at this point to provide suihcient carbon Abetween the oxide particles to hold the residual particles apart, thereby preventing coalescence and agglomeration (sintering). This enables the reduction to go to completion and makes possible handling the materials in solid form throughout. Even a few percent of excess carbon in the coke structure will leave carbon, separating the particles of residual oxide and thereby prevent sintering. Inthe preferred embodiment the excess carbon is sufficient also to provide a residual strength adequate to maintain the physical form of the individual bodies and thereby maintain the porosity and heat-transfer characteristics of the charge up to and following complete reduction.

The difliculty with prior efforts to vsolve the problems involved is that although the reaction can be made to proceed to some extent at temperatures below those at which theV oxide residue is uid and tappable, it will not proceed below the ktemperature range in which the phosphate rock is plastic, and within this range the particles of phosphate rock cohere and coal'esce (sinter) formi'ngV glasses which block off and arrest further reduction. Individual masses cohere to one another and would adhere to furnace structure, refractory walls, grate bars, etc. forming 'systems which cannot be4 successfully handled inpresent industrial equipment.

With respect to the formation off the coke structure throughout which the oxide .particles are disseminated for the maximum initialand residual strength, with minimum carbon, the Voxide particles should beV relatively small, i.e., predominantly passing mesh. With an oxide of these characteristics a satisfactory coke carbon structure cannot be achieved with a coke-forming material consisting exclusively of coking coal, by procedures heretofore available unless the .coking coal is used in amounts that would be uneconomic and would inhibit reaction between thev phosphate rock particles and added silica where added silica is necessary, as hereinafter de veloped.

One method of generating the desired coke carbon 'structure is to admix the oxide with a substance selected from the tars, pitches and asphalts (including the oxidized asphalts) and mixtures thereof. Inasmuch as these materials are residual products of distillation varying within limits, it may not be postulated that all are satisfactory for this purpose. In general those which would be satisfactory as binders for manufacture of carbon electrodes are usable. The range of such materials suitable for this purpose is, however, wider than for electrode manufac ture since the requirements are less severe. An empiric method of evaluating such materials is described in an articlef by Charette and Bischofberger (Industrial & Engineering Chemistry, July 1955, pp. 1412-1415) in which one standard of evaluation is the characterization'factorr Whether a particular material is satisfactory is inl anyY event determinable by a relatively simple test. A sample is compounded in accordance with the instructions of the instant disclosure, briquetted under a pressure of several hundred pounds per square inch to form a briquette, the major dimension of which is not over 1% and heated gradually in a closed, but not Ysealed container, from normal temperatures to 800 C. over a period of about two hours. After cooling in the sealed container the resulting coked briquettes should beV rm and dense, with a `strength in compression of at least 100 lbs. per square inch.

The coke forming Vmaterial and the oxide are rst uniformly mixed. VWith materials that are freely fluid below the temperature of active pyrolysis, the amount of such material should be suicient to occupy the spaces between the oxide particles. For the same reason less coke-forming material is required if the mix is briquetted under pressure. If an excess over this amount is used, it may separate and the carbon subsequently formed in the separated part will not envelop oxide particles or contribute to the reduction. With substances that become only plastic and not freely iluid up to the temperature of active pyrolysis, this limitation does not obtain, but since all such materials are more expensive than sources of carbon, such as coal and coke breeze, the coke-generating material should be used in the minimum amounts that will yield a satisfactory coke structure and the remainder of the carbon supplied by incorporating coke breeze, anthracite, bituminous coal, etc. of substantially the same particle size as the oxide. If this is bituminous coal, it contributes to the bonding elect, and in such case I have been able to achieve a satisfactory coke structure with a substance selected from the tars, pitches and asphalts having a characterization factor 1 as low as about 25.

I have, moreover, been able to form a satisfactory coke structure using bituminous coal alone, by following a novel procedure. In accordance with this, the bituminous coal and oxide are ground together in a state of extreme fmeness for a period of several hours. As charged to the grinder the mixture is grey and the individual particles of coal and oxide are distinguishable. After grinding (preferably ball milling) together for a period of several hours, the mixture is black, individual vparticles'of oxide and coal are no longer separately distinguishable, and the coal present has acquired the property of flowing under great pressure. The exact nature of the change taking place is not yet understood. Whenever by the application of pressure of the order of ten tons per square inch the coal in the mixture is found to be owable, ie., to form a continuous pitch-like substance enveloping the oxide particles, the grinding is discontinued and the entire batch is briquetted under such pressure. Thebriquettes so formed resemble pitch in appearance, with the coal forming a continuous monolithic which envelops the oxide particles. 'Ihe briquettes soformed are coked in a continuously operating retort with top feed and bottom discharge.

With those coke-forming substances which are freely fluid below the temperature of pyrolysis, I am practically limited to carrying out the pyrolysis of the mix in a type of furnace in which the mix is supported in a quiescent state during pyrolysis, such as a coke oven or a broad oven. With the coke oven or broad oven a period of several hours will be required to transfer the heat to those portions of the charge most remote from the heating surfaces. The surfaces should not be heated to a temperature higher than 900 C. and the operation can be concluded and the charge ejected when the portions most remote reach 700 C. With those substances selected from the tars, pitches and asphalts which become only plastic and not freely fluid up to the temperature of pyrolysis, the substance is intimately mixed with the oxide particles in nely divided, solid form and the mix is briquetted under pressure. It is then coked ina continuously operating retort with top feed and bottom dis- 4 charge. The `briquetted charge has better heat-transfer characteristics than those coked in a coke oven or broad l oven and may therefore be gradually heated over a period of about two hours from normal temperatures at the top to -about 800 C. at the discharge end, although longer heating periods and more gradual pyrolysis yield a coke structure of improved strength.

If the coke is in the massive form produced by a coke oven or a broad oven, it should be subdivided to produce a charge through which gas can move freely-for example from about 1" minor dimension to about 3" major dimension. If the coke is in the form resulting from briquetting and continuous coking, this is not necessary.

In the next step the charge so formed is heated out of contact with combustion gases to a temperature at which reduction proceeds with formation of carbon monoxide and'phosphorus in gas phase. The reason for excluding contact with combustion gases is that at the reduction temperature the carbon dioxide and water vapor present in combustion `gases would react with the carbon present, thereby destroying the coke structure. The reduction starts at about V1000 C. but is of low velocity and at this temperature, is not sustained. It proceeds actively around 1l00 C. but the velocity falls off rapidly at this temperature. To obtain the maximum yield at the lowest possible temperature, silica of approximately the same degree of subdivision as the phosphorus ore and in a mol ratio to the OaO present of about 1:1 should be incorporated prior to the coking operation. In this case approximately of the phosphorus present is recoverable at a top temperature of about l260 C. This may be accomplished by holding the charge at about 1200 C. for about two hours, followed by holding it at about 1260 C. for about one hour, or alternatively by raising it gradually from 1100- 1260 C. over a three hour period. At higher Ytemperatures the residence time will of course be shorter. With lesser amounts of silica higher final temperatures are required for full recovery, although even without any added silica, full recovery is obtainable at a inal temperature of about l500 C.

The carbon monoxide and phosphorus produced in gas phase are conducted away and the phosphorus recovered. The residue is removed in solid form. As stated, the excess carbon forms a layer between the oxide particles which holds them apart, inhibiting any tendency of the individual' particles to coalesce into plastic or fluid masses'. Although the residual oxide particles may be plastic, the mixture behaves as a solid throughout and may be nally removed as a solid.v With sufficient excess, the coke structure as such will survive reduction and the individualrmasses can be removed from the heating zone 1n the same physical form in which they were charged.

The following is an example of one application of the process, usmg an oxidized petroleum asphalt as the hydrocarbon binder:

Example 1 The materials used were as follows: (a) Florida phosphate rock containing about 67% -(b) Bituminous coal through 100 mesh. This coal on pyrolysis developed about 68% coke carbon.

(c) Oxidizedpetroleum asphalt about 180"` F. melting point, coking value about 30%, atomic carbon hydrogen ratio about 0,841.0. I i

(d) Silica flour.l Y ""1 The materials Iwere mixed at a temperature above the melting point of the asphalt in the following proportlons:

At the conclusion of the mixing the resulting mix was dark-colored and plastic. The mix was coked by gradual heating up to a red heat over a three hour period, in a metal container with a loosely tting cover.

At the conclusion of the coking the net weight of the residual mixture was 712 grams. The residue was hard, resembling coke in physical appearance although considerably denser, with a compressive strength well over 100 lbs. per square inch. Allowing for about 2% (6 grams) of ash in the coal and about 3% (13.80grams) of moisture in the phosphate rock, this calculates to a carbon content of about 212 grams. 43.8 grams analyzing 9.04% (4.85 grams) of phosphorus in the form of `small lumps was heated in a quartz tube tted with a glass condenser at the outlet end. A gentle stream of CO was passed into the tube at the inlet end to carry the products of reduction into the condenser. The charge' was heated to a top temperature of about 1250 C. The evolution of phosphorus appeared to be complete within the first 2 hours, although the heating was continued for a total period of 51/2 hours. At the conclusion of the run the total loss in weight of the charge was 25% and the phosphorus content 0.148 gram, corresponding to a recovery of 96%. The individual lumps of the charge retained their original form. They resembled coke in appearance. They had not fused or adhered either to one another or to the quartz tube and retained a large part of their original strength in compression.

The following isan example of the application of the process using a so-called aromatic tar as hydrocarbon binder: f

Example 2 The materials used were as follows:

(a) Florida phosphate rock containing about 68% tricalcium phosphate or its equivalent in P205 content and running about the same in particle size as that of Example l.

(b) 'Bituminous coal, same as in Example l.

(c) Aromatic tar. This is a product of the petroleum industry. It is a residuum from the catalytic cracking olf petroleum. It has a Coking value of about 25 and an atomic carbon-hydrogen ratio of about 0.95 :1.0.

(d) Silica flour.

The materials were mixed in the following proportions.

Grams Phosphate rock 180 Silica 60 Bituminous coal 60 Aromatic tar 35 Total 3 3 5 At the conclusion of the mixing the mix was darkcolored and slightly cohesive. The mix was heated in a metal container with a loosely fitting cover over about a three hour period, to a maximum temperature of 760 C. At the conclusion of the run the coke had a compressive strength well over 100 lbs. per square inch. The carbon content of the coked material was about 18.62%. Lumps of the material yso produced were then heated in a combustion tube similar to that described in Example l, in a ceramic carrier, for a period of about 2 hours, to a maximum temperature of about 12.50 C. At the conclusion of the run the total loss in weight was 34%. The lumps retained their original form andv showed no evidences Example 3 The materials used were as described in Example 2. The materials were mixed in -the following proportions:

Grams Phosphate rock Y A y 180 Bituminous coal 60 Aromatic tar y 35 Total 275 The resulting mix was coked in the same mannerras described in Example 2. The net loss on the coking was 19% of the charge. The coked charge had a compressive strength well over lbs. per square inch. The carbon content of the coked `charge was 21.09%.

The reduction was carried out in the manner described in Example 2 except that the temperature of reduction vwas about 1500u C. 'Ihe recovery of phosphorus was 96% by weight.

In each of these runs the residual lumps were in the same form as the originals, still retaining some strength in compression and showing no cohesion or adhesion.

The following run was carried out for the purpose of showing the elect of eliminating the added silica While maintaining a lower temperature:

Example 4 The materials used were as described in Example 1. The materials were mixed at a temperature above the melting point of the asphalt inthe following proportions:

Grams Phosphate rock 460 Bituminous coal 15 0 Asphalt 15 0 Total 760 At the conclusion of the Coking, the net Weight of the residual mixture was 610 grams and 4the residual coke resembled that described in Example 1. 51 grams of the charge so prepared, in the form of small lumps, was heated under conditions as described in Example 1, for a total period of 61/2 hours although the evolution of phosphorus was complete in about 2 hours. The maximum temperature obtained in the run was 1260 C. The yield of phosphorus was only 64.2% by weight. The individual lumps of the charge retained their. original form resembling coke in appearance. They had not fused or adhered either to one another or to the ceramic boat in which the charge had been contained, and retained a large par-t of their original strength in compression.

Example 5 Grams Phosphate rock 360 Silica Coking coal 100 'Iiotal 580 The materials were ball milled together for a period of approximately` 12 hours, following which they were briquetted in a hydraulic press under a pressure of approximately 15 tons per squareA inch. The resulting briquettes were extremely firm and dense. The exterior had a smooth surface resembling pitch in appearance and no oxide particles were visible.

Briquettes of the material were placed in a container with a looselyitting cover and in this container carried from normal temperatures to a temperature of about 760 C. over a period of about 1 hour. 'Ihe loss on coking was about 6.4% and the resulting briquettes had a carbon content of 11.68%. The coke briquettes were extremely rm and dense and had a strength in compression of several hundred pounds per square inch.

86.7 grams of the briquettes in an Alunden carrier were charged into a silica combustion tube and heated to a top temperature of about 1250o C. over a period of two hours.V Upon cooling and removal, they were still in `the original form resembling bodies of coke in appearance although somewhat low in residual strength.

The loss of weight on retorting was 31% and the carbon content of the residue was 3.02%. The phosphorus content of the briquettes before retorting was 9.5% and of the residue 1%, corresponding to a liberation of 93% of the contained phosphonus.

Example 6 (d) Coal tar pitch, melting point 10S-115 C., cok-` ing value about 43%, atomic carbon-hydrogen ratio about 1.70:l.0.

The materials were mixed in the following proportions: Y

, Grams Phosphate rock 360 Silica 120 Fluidized coke 70 Pitch 50 Total 600 The materials were briquetted in a hydraulic press under pressure of several hundred pounds per square inch, following which they were coked by carrying them froml normal temperatures to about 760 C. in a closed container over a period of about 1 hour. The loss of weight on carbonizing was 6.43%.

Three briquettes of a total weight of 146.5 grams were charged into a porcelain tube of an inside diameter of 1%. A porcelain reflector was placed on either side of the three briquettes and the tube heated in a combustion furnace. The tube was connected to a glass condenser and a slow stream of nitrogen was passed through the porcelain tube in the direction of the'glass condenser to prevent condensation of phosphorus in the end of the porcelain tube which was not connected to the glass condenser. The temperature in the tube itself was not measured. The temperature in the furnace was measured and it was assumed that the differential between the furnace temperature and that inside the porcelain tube was not significant. Some phosphorus was observed in the condenser at a furnace temperature of about 1000 C. The temperature in the furnace was gradually raised from this to a final temperature of about 1260 C. over a period of about 21/2 hours. After cooling the porcelain tube was disconnected from the condenser and tilted 8 slightly, whereupon the residue slid forward to the exit end of the tube. The carbon content of the briquettes charged was 14.52% and of the residue 6.74%. The residue had disintegrated to a powder but showed no cohesion or adhesion. The loss on retorting was 29.4%. 87% of the total phosphorus content of the ore was liberated in retorting.

Example 7 In this case the materials used were as follows:

(a) Phosphate rock, same as in Example 4.

(b) Silica, same as in Example 4.

(c) Bituminous coal, same as in Example 4.

The materials were mixed in the following proportions:

The materials were ball milled together for a period of approximately l2 fhours, following which they were briquetted in a Ihydraulic press under pressures of about 15 tons per square inch. The resultant briquettes were rm and dense, resembling pitch in appearance. No oxide particles were visible.

The briquettes were coked by heating them in a closed container from normal temperatures to a top temperature of about 760 C. over a period of one hour. The loss'in weight in coking was 6.8%. The resulting coked briquettes were rm, dense and very strong.

Six briquettes of a total weight of 219.56 grams were charged into a porcelain tube of an inside diameter of 1% 4with a porcelain reflector at either end of the charge. The porcelain tube was connected to a glass condenser and a slow current of nitrogen passed through from the other end of the porcelain tube. A trace of phosphorus was observed in the condenser at a temperature in the furnace of about 1000 C. The temperature was gradually raised for a period of about three hours to a top temperature of 1260 C.' After cooling the con- 'denser was removed and the porcelain tube tilted. The

briquettes slid out in exactly the same form as charged. There was no cohesion or adhesion or sintering and they still retained substantial residual strength. The loss in weight on retorting was 30.4%. The amount of phosphorus picked up in the condenser was 18.89 grams but there was still considerable phosphorus which had condensed in the inlet end of the porcelain tube and some had, of course, passed olf as a fume in the exit nitrogen gas. 95.6% of the phosphorus content of the ore was liberated in the retorting operation. The carbon content of the briquettes charged was 14.28% and of the residue 6.30%.

Referring to Figs. 1 and 2, 1 designates a retort, including heating zone 2, defined by refractory walls 3 and 4. Wall 3 `is heated by burner 5 ldischarging into oven 6, which feeds communicating ues 7, 8, 9 and 10, waste gases escaping through stack 11. Wall 4 is similarly heated by burner 12 discharging into oven 13 which feeds communicating flues 14, 15, 16 and 17, waste gases escaping through stack 18.

Charge for the heating zone is rst deposited in bin 21, from.|which Iby opening poppet 22 controlled by tube 2-3, the charge is dropped into bin 24. From bin 24 the charge may be dropped into zone 2 by opening poppet 25 controlled by rod 26.. In this way it is possible to charge zone 2 without escape of gas therefrom. Any gas produced in 2 is withdrawn through duct `31 to suit# able condensers (not shown). Exhausted residue may be withdrawn-from the lower end 32 of yzone 2 by operation of the internally cooled revolving grate bars 33 turned by any suitable means diagrammatically indicated by 34Y (Fig. 2). The residue discharged by the gratebars drops into space 35, from which it may be continuously withdrawn by wor-n1 conveyor 36. A gas may be passed into spacel 35 through valved pipe 37. The heating zone, ilues and bins are contained in common jacket 38. k

A charge is rst com-pounded in accordance with the formula set forth in Example 2, and coked in a broadoven to a maximum temperature of about 900 C. at the heating surface and a minimum temperature of about 800 C. After coking and quenching it is reduced to about 1" minimum ydia-meter, and so fed through bins 21 and 24 to zone 2. It is heated in zone 2 by operation of burners and 12 to a top temperature `of Iabout 1260 C. in the lower end 32 of zone 2. The bars 33 are set to turn at a rate providing a dwell of at least 3 hrs. at a temperature between 1100 and 12.60 C. Exhausted -residue in solid form is withdrawn by operation of worm l conveyor 36. A small amount of gas inert in relation to the reactants, for example car-bon monoxide, hydrogen or nitrogen in amount suicient fto maintain a slight plus pressure in space 35 and prevent condensation of phosphorus therein, is continuously introduced through valved pipe 37. The carbon monoxide and phosphorus evolved are withdrawn through educt 31 into condensers in which the volatile inorganic .compounds are first condensed, following which the phosphorus isA condensed. 'Ilhe residual carbon monoxide may be utilized -as fuel 'for drying, Igrinding, etc. in earlier stages of the process.

Referring now to Figs. 3 and 4, S1 designates an electric Afurnace adapted for use in one embodiment of my invention. This includes shell 52 carrying refractory lining 53, deiining reduction zone 54. Material may be continuously withdrawn from the lower end 55 of the reduction zone by means of a series of grate bars 56. Every section of the furnace above the *line 4'-4 is circular in outline, Whereas the sections below that are rectangular, as indicated in Fig. 4. The grate bars may be turned from the exterior of the furnace by any suitable means diagrammatically indicated by 57, driven by any suitable means, such as motor 58. Material may be continuously removed yfrom the bottom 59 of the furnace by worm conveyor 60 discharging to a point exterior of the shell S2 through a suitable duct 61 which in turn discharges into chute y62. A gas may be continuously introduced into the bottom 59 through valved pipe 63. Charge -for the reduction zone is rst deposited in bin 64, from which, by opening poppet 65 controlled by tube 66, the charge drops into bin 67. From bin 67 a batch vcharge may be dropped into reduction zone 54 by opening poppet 68 controlled by rod 69. In this way it is possible to charge reduction zone 54 without escape of gas therefrom. Any gas produced in the reduction zone 54 is withdrawn through duet 7,1 to suitable condensers (not shown). In practice the furnace is charged to the approximate level indicated by line 75. The charge in the furnace may be heated by a number of electrodes, such as 76, carried by electrode holder 77, which electrode enters the furnace through stuing box 78v and electrode 81 carried by electrode holder 82, which electrode enters the furnace through stuing box `83.- 'Dwo such electrodes may be provided -for single phase operation and three electrodes placed at equal horizontal angles from each other for three phase operation.

In the operation of this apparatus a charge of the material specified in Example 4 is compounded in accordance with the following formula:

Parts Phosphate rock c 360 Bituminous coal l' 120 The materials are ball milled together for a period llof at least 12 hours and until a sample of the material when briquetted under a pressure of about 15 tons per square inch showed that the coal has developed the property of flowing under high pressure. Whenever this point has been reached the entire char-ge is briquetted under a pressure of about 15 tons per square inch and the individual briquettes so produced are coked in a continuous coker, in which they are carried from normal temperatures to a top temperature of about 800 C. over a period of approximately 2 hours. After coking and while still at elevated temperature, the briquettes are fed through bins 64 and 67 to reduction zone 54 up to the level indicated byline 75. It is heated in the furnace by the passage of current through the charge from electrodes 76 and 81 to a maximum temperature of about 1500 C. Owing to the fact that the charge remains solid, the heat is generated principally by conduction within the charge between the individual masses composing the charge. Phosphorous and carbon monoxide are evolved and conducted away through duct 71 to suitable condensers, the operation of which corresponds to present commercial practice in the electric furnace reduction of phosphate ores. The reduction will be substantially completei-n -a dwell of about one hour at the top temperature of about 1500 C. The grate bars 56 are operated to maintain this dwell and fresh char-ge is added intermittently lfrom bins 64 and `67 `to maintain approximately the upper level 75 of the `charge in the reductiony zone. A small amount of inert gas, such as carbon monoxide, hydrogen or nitrogen, is continuously introduced through valved pipe 63 to maintain a positive pressure in the lower end 59 of the furnace, to thereby prevent the descent of phosphorus vapors into this space. The briquettes retain their original form during the heating and while passing downwardly out of the heating zone. During this phase they are still in solid form although the individual particles may still be plastic. The coke structure prevents any sintering or agglomeration and causes the entire briquette to behave as a solid. In the lower end of the refractory enclosure the residual lbriquettes are cooled by contact with the up-flowing inert gas, so that at this point both the carbon and the residual oxide particles are in true solid phase. The briquettes will of course be broken in passing through the grate bars. The exhausted residue in the form of relatively small particles, as delivered by the grate bars 56, is continuously removed by operation of the worm conveyor 60, discharging through pipe 61 into chute 62, by which it is removed from the system.

In this case, as hereinabove stated, the residualoxide after burning off the excess carbon, is principally calcium oxide and may therefore be marketed as lime. It will of course be understood that the same general method of operation may be employed with a charge compounded in accordance with Example 2, coked and prepared in the same manner, except that in this case reduction will take place at a relatively lower average temperature in `the charge and with substantially less consumption of electric power.

1. Process of winning phosphorus from oxygenated ores containing the same which comprises forming a briquetted coke throughout which the ore is disseminated in the form of particles in a supporting structure of carbon, thereafter heating the coke so formed in a heating zone -to a temperature at which reduction proceeds with formation of carbon monoxide and phosphorus in gas phase while maintaining same substantially free from direct contact with combustion gases and free from substantial electric arc heating, maintaining such tem .perature until at least the major part of the phosphorus content of said ore has been liberated, said coke containing sucient excess carbon over that consumed in the reduction to substantially prevent deterioration of the briquettes during the reduction and to hold the residual particles of said ore apart and prevent lagglomeration of the same, conducting away said carbon monoxide and phosphorus in gas phase, separating phosphorus 11 therefrom and removing residual carbon and residual ore particles from said heating zone, in solid form,

2. Process according to claim 1 in which said particles predominantly pass a 100 mesh screen.

3. Process according to claim 1 in which formation of said coke comprises mixing the said particles With a substance selected from the tars, pitches and asphalts and mixtures thereof, thereby forming a mixture, thereafter heating the said mixture progressively through the temperature range in which pyrolyss occurs, thereby forming a coke throughout which said particles are disseminated.

4. Process of Winning phosphorus from oxygenated ores containing the same which comprises forming individual briquettes of coke throughout which the ore is disseminated, in the form of particles, in a supporting structure of carbon, maintaining a charge of said bn'- quettes Within a space defined by a refractory setting, said coke having a strength in compression adequate to withstand the crushing stress of superincumbent charge and maintain the form of said briquettes, indirectly heating such charge in a heating zone in said setting to a temperature at which reduction proceeds with formation of carbon monoxide and phosphorus in gas phase while maintaining same substantially free from direct contact with combustion gases, maintaining such temperature until at least the major part of the phosphorus content of said ore has been liberated, said coke containing sufficient excess carbon over that consumed in the reduction to substantially prevent deterioration of the briquettesY during the reduction and to maintain the residual particles of said ore apart and prevent agglomeration of the same, conducting away said carbon monoxide and phosphorus in gas phase, separating phosphorus therefrom and removing residual carbon and residual ore particles from said heating zone, in solid form.

5. Process according to claim 4 in which said particles predominantly pass a 100 mesh screen.V

6. Process according to claim 4 in which formation of said coke comprises mixing the said particles with a substance selected from the tars, pitches and asphalts and mixtures thereof, thereby forming a mixture, thereafter heating the said mixture progressively through the temperature range in which pyrolysis occurs, thereby forming a coke throughout which said particles are disseminated. Y

7. The continuous process of winning phosphorus from oxygenated ores containing the same, which comprises forming individual briquettes of coke throughout which the ore is disseminated in the form of particles in a supporting structure of carbon, maintaining a charge of said briquettes within a space deued by a refractory setting, said coke having a strength in compression `ade quate to withstand the crushing stress of superincumbent charge and maintain the form of said briquettes, indirectly heating said charge in a heating zone in said setting to a temperature at which reduction proceeds with formation of carbon monoxide and phosphorus in gas phase while maintaining same substantially free from direct contact with combustion gases, maintaining such temperature until at least the major part of the phosphorus content of said ore has been liberated, said coke containing suicient excess carbon over that consumed in the reduction to substantially prevent deterioration of the briquettes during the reduction and to hold the residual particles of said ore apart and prevent agglomeration of the same, conducting away said carbon monoxide and phosphorus in gas phase, separating phosphorus therefrornadding fresh briquettes to said charge at one 12 point and 4removing residual carbon and residual ore particles from said heating zone, at another point.

8. Process according toclaim 7 in which said particles predominantly pass a mesh-screen.

9. Process according tok claim 7 in which formation of said coke comprises mixing the said particles with a substance selected from the tars, pitches and asphalts: and mixtures thereof, thereby forming a mixture, thereafter heating the said mixture progressively through the temperature range in which pyrolysis occurs, thereby forming a coke throughout which said particles are disseminated.

10. Process according to claim 7 in which said charge is heated lby the application of combustion heat to the exteriorsurfaces of said refractory setting.

1,1. The continuous process of Vwinning phosphorus from oxygenated ores containing the same which comprises forming individual briquettes of coke throughout which the ore is disseminated, in the form of particles, in a supporting structure of carbon, maintaining a charge of said briquettes within a space defined by a refractory setting, said coke having a strength in compression adequate to withstand the crushing stress of superincumbent charge and maintain the form of said briquettes, heating such charge in a heating zone in said setting to a temperature at which reduction proceeds with formation of carbon monoxide and phosphorus in gas phase while maintaining same substantially free from direct contact with combustion gases and free from substantial electric arc heating, maintaining such temperature until at least the major part of the phosphorus content of said ore has been liberated, said coke containing suicient excess carbon over that consumed in the reduction to substantially prevent deterioration of the briquettes during the reduction and to hold the residual particles of ore apart and prevent agglomeration of the same, and to maintain the initial form of said briquettes. throughout said reduction, conducting away said carbon monoxide and phosphorus in gas phase and separating phosphorus therefrom, adding fresh briquettes to said charge at the top of said heating zone and removing residual briquettes reduced in phosphorus content from said heating zone, at the bottom thereof.

12. Process according to claim 11 in which said particles predominantly pass a 10() mesh screen.

13. Process according to claim 11 in which formation of said coke comprises mixing the said particles with a substance selected from the tars, pitches and asphalts and mixtures thereof, thereby forming a mixture, thereafter heating the said mixture progressively through the temperature range in which pyrolysis occurs, thereby forming a coke throughout which said particles are disseminated.

14. Process according to claim 11 in which said charge is heated by theapplication of combustion heat to the exterior surfaces of said refractory setting.

15. Process according to claim 11 in which said charge is heated in said heating zone by electric resistance heating by the passage of electric current through said briquettes from electrodes in contact therewith.

References Cited in the file of this patent UNITED STATES PATENTS 

1. PROCESS OF WINNING PHOSPHORUS FROM OXYGENATED ORES CONTAINING THE SAME WHICH COMPRISES FORMING A BRIQUETTED COKE THROUGHOUT WHICH THE ORE IS DISSEMINATED IN THE FORM OF PARTICLES IN A SUPPORTING STRUCTURE OF CARBON, THEREAFTER HEATING THE COKE SO FORMED IN A HEATING ZONE TO A TEMPERATURE AT WHICH REDUCTION PROCEEDS WITH FORMATION OF CARBON MONOXIDE AND PHOSPHORUS IN GAS PHASE WHILE MAINTAINING SAME SUBSTANTIALLY FREE FROM DIRECT CONTACT WITH COMBUSTION GASES AND FREE FROM SUBSTANTIAL ELECTRIC ARC HEATING, MAINTAINING SUCH TEMPERATURE UNTIL AT LEAST THE MAJOR PART OF THE PHOSPHOROUS CONTENT OF SAID ORE HAS BEEN LINERATED, SAID COKE CONTAINING SUFFICIENT EXCESS CARBON OVER THAT CONSUMED IN THE REDUCTION TO SUBSTANTIALLY PREVENT DETERIORATION OF THE BRIQUETTES DURING THE REDUCTION AND TO HOLD THE RESIDUAL PARTICLES OF SAID ORE APART AND PREVENT AGGLOMERATION OF THE SAME, CONDUCTING AWAY SAID CARBON MONOXIDE AND PHOSPHORUS IN GAS PHASE, SEPARATING PHOSPHORUS THEREFROM, AND REMOVING RESIDUAL CARBON AND RESIDUAL ORE PARTICLES FROM SAID HEATING ZONE, IN SOLID FORM. 